I'd consider buying a Minimig too, but as far as I know you cannot yet attach any type of hard-drive (or other mass storage device to it). There's only the SD card which can act like a floppy (or hold many floppy images).
As it is, (as far as I understand), the Minimig just does a pretty good job of emulating an ECS Amiga 500, but not much beyond that.
I've seen demos of an AGA Minimig - essentially a MiniMig A1200, but I don't think that's been released or perfected.
Too bad, because I certainly WOULD buy a Minimig if it had AGA, real or virtual hard drive support, RTG graphics support, more RAM and a 68030 or 040 emulated CPU. Essentially a "big box" Amiga Minimig (A3000/A4000).
I was very impressed by the Minimig when it first came out (what, like five years ago now), and understood that a basic A500 Minimig was a great achievment, but I thought we'd be at the A4000 level with it now.